A search for strongly-lensed quasars in the Sloan Digital Sky Survey.

摘要

This work describes the methods and status of a search for gravitationally-lensed quasars in the dataset of the Sloan Digital Sky Survey (SDSS). I present a series of selection criteria which are designed to identify gravitational lens candidates among SDSS quasars. These selection criteria are underpinned by a Point Spread Function fitting procedure which models the SDSS atlas images of quasars as a pair of point sources.; These selection criteria are applied to a sample of 34605 spectroscopically-confirmed z > 1 SDSS quasars. 260 candidates are selected. The existing follow-up observations for a number of interesting candidates are reviewed. 12 of the 260 candidates are confirmed or probable lens systems. These objects set a lower limit on the observed lensing rate of 1.9 × 10−4 (95% confidence level).; I present a technique for creating simulated SDSS images. These simulated images are used to characterize the selection function of the selection algorithm used to identify lens candidates. For the median SDSS quasar, the selection algorithm is able to identify equal flux pairs of point sources down to separations of 0″.6 and with flux ratios up to 16:1 at separations greater than 1″.2. I present a method for verifying the statistical accuracy of simulated images through comparison to real SDSS data.; I show that selection effects associated with the SDSS star-galaxy separator will cause the sample of high-redshift SDSS quasars to be strongly biased against lenses. I use a simple model of the lensing population to predict the effects of the selection function for the main quasar sample and show that ∼35% of lensed quasars will be deselected. Finally, I introduce a technique for correcting for the heterogenous nature of the existing follow-up observations of gravitational lens candidates, and apply this technique to predict that the observed lensing rate of SDSS quasars is 1.6 × 10 −3 (∼1 in 600), and that the true lensing rate is 2.5 × 10−3 (∼1 in 400).